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Old 16th January 2008, 07:34 PM   #1
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Default Suggest KT88 Push-Pull schematics, please.

Hi,

I am new to HIFI tube amps. I have just built two guitar amps. Still I havenīt decided myself if I will go with SE or PP. I havenīt found enough information where are the differences in sound described between SE and PP. I just read hear for yourself and then decide. Problem is I do not have any chance to go somewhere and listen to tube amp. If I will go with SE then with Mikael Abdellahs schematics, but I am still not sure what scheme should I use for PP.

I already have transformer for one PP monoblock or one SE stereo: 350-0-350 @ 250mA.

Can you please suggest good sounding KT88 push-pull schematics with these tubes? - ECC81,2,3, ECC88.



Thank you very much.
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Old 16th January 2008, 08:05 PM   #2
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I'd look at the Poseidon driver for the Dynaco Mark III amplifier:
http://www.diytube.com/phpBB2/viewtopic.php?t=923

There's schematics included in the user's manual. It takes a 12AX7 and a 12AU7 (ECC83, ECC82) so it matches your tube request. The power transformer specified is a 400-0-400 volt unit, so I'm not sure the transformer you have is quite there. Maybe if you run it with solid state diode rectification instead of using the 5AR4.

Are you sure you really want to tackle a pair of KT88 monoblocks for your first hifi tube amp? The output iron gets expensive. I'd be tempted to look at any one of the many fine PP or SE designs for the EL84 (6BQ5) output tube. You ought to be able to build both a PP and a SE amp (stereo, of course) for less than the price of a pair of KT88 monoblocks. Then you really could listen to them both for yourself.
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Old 16th January 2008, 08:07 PM   #3
Svein_B is offline Svein_B  Norway
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A link to the Mikael Abdellahs schematics make it easier for others to follow the discussion: http://diyaudioprojects.com/Tubes/KT88/

A EL34/KT88 PP alternative without too much complications might be Allen Wrights PP-1C: http://www.vacuumstate.com/schematics.htm
Simple 2-stage design, no GFB (unless you want it).

SveinB
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Old 16th January 2008, 09:03 PM   #4
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Quote:
Originally posted by Ty_Bower
I'd look at the Poseidon driver for the Dynaco Mark III amplifier:
http://www.diytube.com/phpBB2/viewtopic.php?t=923

There's schematics included in the user's manual. It takes a 12AX7 and a 12AU7 (ECC83, ECC82) so it matches your tube request. The power transformer specified is a 400-0-400 volt unit, so I'm not sure the transformer you have is quite there. Maybe if you run it with solid state diode rectification instead of using the 5AR4.

Are you sure you really want to tackle a pair of KT88 monoblocks for your first hifi tube amp? The output iron gets expensive. I'd be tempted to look at any one of the many fine PP or SE designs for the EL84 (6BQ5) output tube. You ought to be able to build both a PP and a SE amp (stereo, of course) for less than the price of a pair of KT88 monoblocks. Then you really could listen to them both for yourself.

I have bunch of KT88, thats why I want to stick with them. EL84 - SE would not give enough power for my speakers. EL84 PP sounds interesting...maybe next project.

Anyway I have found VERY interesting reading about SE vs PP. Here are the links:
http://homepage.mac.com/tlinespeaker...v-PP-Part1.pdf

http://homepage.mac.com/tlinespeaker...v-PP-Part2.pdf
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Old 16th January 2008, 09:03 PM   #5
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What about this schematics?

http://www.amplimo.nl/download/pubs/hqpp-50/hqpp50.pdf

Does it look like it should sound very good?
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Old 17th January 2008, 10:22 AM   #6
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Quote:
Anyway I have found VERY interesting reading about SE vs PP. Here are the links:
Excellent articles.

I think It misses one essential fact about the difference between PP and SE.
Most people who build SE amps know that the benefits will come from the compromises (ie class A operation, extreme attention to component selection, usually the choice of real low rp triode's, low or zero gNFB). I think if people making PP amps applied the same compromises - they would end up with designs that can quite easily beat most SE designs.
Unfortunately most people start off from a whole different set of compromises which are attached to such designs as the Williamson circuit. It becomes almost inevitable that the PP will fail to outperform the SE amps in all but the measurements and power catagories.
Design your PP amp as if it was a SE amp and I personally think there can be no argument about which is best.

Shoog
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Old 17th January 2008, 07:19 PM   #7
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Quote:
Originally posted by Shoog
I think It misses one essential fact about the difference between PP and SE.
Most people who build SE amps know that the benefits will come from the compromises (ie class A operation, extreme attention to component selection, usually the choice of real low rp triode's, low or zero gNFB). I think if people making PP amps applied the same compromises - they would end up with designs that can quite easily beat most SE designs.
Unfortunately most people start off from a whole different set of compromises which are attached to such designs as the Williamson circuit. It becomes almost inevitable that the PP will fail to outperform the SE amps in all but the measurements and power catagories.
Design your PP amp as if it was a SE amp and I personally think there can be no argument about which is best.
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Old 17th January 2008, 07:23 PM   #8
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I design PP amps with the same attention to details (and with the same education and experience), but SE anyway sounds more natural (especially with very deep and with no GNFB).

edit: and PP always give more power per each consumed watt.
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Old 18th January 2008, 08:15 AM   #9
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It quite interesting that in the second article he is very complementary of PP toroidal output transformers, because of their low hysteresis losses. This is the area where most PP amps seems to lose out to SE amps, in the area of low volume listening and fine detail blurring. So it would seem that the use of Toroid's can make up for most of the deficiencies of PP amps.

All of my home built PP amps have toroidal outputs and have excellent detail and play well at low volumes.

Shoog
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Old 17th October 2011, 09:14 PM   #10
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Default KT88 PP schematic

This can be built as aTriode, pentode or ultralinear



Go to this address

Vintage data

or google

"A 100W power amplifier" by A. Kenneth Olson, from 1955 Radio & Television News, reprinted by Chicago transformer (1.7MB PDF file)

Last edited by lugnut; 17th October 2011 at 09:32 PM.
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